[/size]How to check resistance (continuity) in a component-[/color][/size]A Digital Multi-meter (Ohmmeter) is needed for testing components:An ohmmeter can be used to directly measure an unknown resistance R.This is the simplest way to measure resistance. It is important to realize that an ohmmeter can not be used when the resistance is connected in a circuit and a current is flowing through it!

[/color]Typical Digital Multimeter [/size][/font]

Scale

Measurement Range

in words

ohms (Ω)

2M

two megohmtwo million ohms

0-2,000,000

200K

two hundred kilohmtwo hundred thousand ohms

0-200,000

20K

twenty kilohmtwenty thousand ohms

0-20,000

2K

two kilohmtwo thousand ohms

0-2,000

200

two hundred ohm

0-200

Setting up the meter

To use the multi-meter as an ohmmeter turn the selector dial to point to the ohms range. On some models (usually not on the cheaper ones) the meter will have a single ohms setting and will auto select the best range for you.To measure resistance you must connect the test leads to the sockets labeled 'COM' and 'Ω'. These may be in different positions on your meter but the labeling should be the same.Without anything connected between the test leads the display will give an out of range indication (-1 in this case) to show that the resistance is too large to measure. In effect, you are trying to measure the resistance of the air between the two inputs, which is very large.Taking measurements

To check the meter is working touch the leads together and the display should read 0.0 Ω. It may read slightly higher, e.g. 0.3 Ω. This is the resistance of the test leads themselves.Turn the selector dial to the lowest resistance range that gives a valid reading.In this case the resistance wire has a resistance of 4.2 Ω.[/size]Accuracy[/color]

The overall accuracy of the reading will depend upon the multi-meter model. The more expensive the meter the better the accuracy will be. For a cheap meter the accuracy is typically in the region of +/- 1% of the displayed value. Check in the manual for the accuracy of your model.It is important to select the correct measurement range. In the above example if the 2 kΩ range is selected the display will read .004 kΩ and the decimal place will be lost. If the dial is set to 20 kΩ the display may read 0.00 kΩ! Always turn the dial down to the lowest range to get the best accuracy. [/size][/font]

Electricity is a basic part of nature and it is one of our most widely used forms of energy. ]Atoms are the building blocks of everything we know. They are so small that to see a material containing millions of them would still need a microscope.

The center of an atom is called the nucleus. It is made up of particles called protons and neutrons. The nucleus is surrounded by minute particles called electrons that move around. If we concentrate on just the electrons this is the part of the atom that we can call electricity. In some materials, electrons are tightly bound to the atoms.(insulating material). This means they don't move very much and they cannot conduct electricity very well. In other materials like metal some electrons are very loose and move easily. (conductive material) They have electrons that can detach from their atoms and move around the structure of the material. These are called free electrons. The moving electrons transmit electrical energy from one point to another. Electrons flow through wires, but they never leave, they just move. For this reason you need something called a circuit. To create an electrical force or movement a generator, alternator or battery is often used relying on magnetism or chemicals to push electrons around. It is not so much pumping the electrons out of the wire though, as simply forcing them all to move along it. So the electrons being pushed out one side of a piece of wire and a new electron follows behind it.In magnetism, most of the electrons at one end are spinning in one direction. At the other end electrons are spinning in the opposite direction. This is unlike other materials as usually electrons are in balance spinning 50% either way along the whole structure. For this reason magnets can be used to make electricity. Moving magnetic fields can pull and push electrons and start moving electrons in a circuit.

A water analogy is often used to help describe how an electrical circuit works. Consider a water pump driving water through a closed loop of piping. The pump never runs out of water (any more than an electrical circuit runs out of electrons) since the water circulated by the pump pushing against the water already in the pipe until it arrives back to the pump. So now we have this energy moving around wires we can begin to control it and use it for our own advantage

Electricity is made in Power Stationsby huge generators powered by coal, nucleur, natural gas, water or even wind. The basic principle of a generator has two main components: a rotating magnet called the “rotor” which turns inside stationary coils of copper wire called the “stator.”

When the rotor rotates through the magnetic field, it generates a flow of current through the copper coils of the stator. Generating plants must use some form of energy or fuel to turn the rotor mentioned above. Electricity is produced, sent through very high voltage transmission lines to substations. At substations, the voltage of the electric power is lowered. Voltage is the force that pushes electricity along wires. Then, the power is sent to your neighborhood through distribution lines located underground or on poles. After electricity is produced at power plants it has to get to the customers that need the electricity. The electricity first goes to a transformer at the power plant that boosts the voltage up to 100,000's of volts. When electricity travels long distances it is better to have it at higher voltages as it can be transferred more efficiently this way.The long thick cables of transmission lines are made of copper or aluminum because they have a low resistance. Some of the electrical energy is lost because it is changed into heat energy. High voltage transmission lines carry electricity long distances to a substation.The power lines go into substations near businesses, factories and homes. Here transformers change the very high voltage electricity back into lower voltage electricity.From these substations , electricity in different power levels is used to run factories, streetcars and mass transit, light street lights and stop lights, and is sent to your neighborhood.Electricity enters your home or premises through a meter. It then goes to the circuit panel or control panel which then distributes the different circuits that power you house. Traditionally, the UK has had a 240 electrical supply since the 1960s. Continental Europe had a 220V, and Ireland a 230V, supply. The USA and Canada are supplied by 120 volts mains connection.

Electrons need something to make them move from atom to atom through a circuit. When electrons are flowing, there has to an electrical force somewhere pushing the electrons. Without a push everything would stay relatively static and we would have no flow of energy. This is what is know as voltage. Voltage is measured in volts. The supply of voltage to domestic and small commercial premises varies in different countries and it is essential to know this. In general you can split it up into two parts of the world: 120 and 220 Volt; (USA) 230 Volt (Europe & Asia)

If volts are the force pushing electrons throught metal, amperes or amps for short is the amount of current flowing in a circuit. The more current flowing, the higher the amps. This flow of electrical current develops when electrons are forced from one atom to another. Current is a measure of the rate of electron flow through a material. Electrical current is measured in units of amperes or "amps" for short. Thinking of electricity as like water, and a wire as like a hose is a popular analogy. How would you measure the water coming out of the hose? There are two ways: The pressure pushing the water (voltage) The amount of water that flows through the hose every second (Amps)

The latter would be the most comparable to the measure of amps running through a cable. A multimeter can be used to test how many amps are flowing through a wire at a given time.

Watts are a measure of the rate at which electricity does its work or provides energy.e.g, the power used to run an electric fire could be 2000 watts. Watts (W) are the units in which electric power is commonly measured.Wattage is calculated by using the following equation: Watts = Volts x AmpsThe electricity in your home is 120 volts depending where you are in the world. A light bulb for example operates at 1 amp. If we use the above equation 120(volts) x 0.5 (amps) = 60 Watts

According to the equation for power, multiplying these two numbers gives the bulb's wattage, which in this case is 60 watts.The wattage tells you the power of the bulb, or the rate at which energy is being delivered. The higher the wattage of bulb, the brighter the bulb and the more power it uses, also the more expensive it is to run.